Funds are requested to continue our studies of the representation and processing of spatially distributed information in the somatosensory system. Two broad aims are identified for the next five years. The first is to establish with certainty which afferent fibers are responsible for spatial form processing and which central neurons are activated by those fibers; evidence points to the SAI system. Experiments will first be conducted to determine the conditions for selectively activating the SAI, RA and PC systems. Knowledge gained from those experiments will be used in psychophysical experiments to determine the function served by each of the afferent systems and in neurophysiological experiments to determine the submodalities driving neurons in SI and SII cortex. The second broad aim is to understand, in precise detail, the spatiotemporal processing functions of individual neurons in the pathways responsible for tactile form recognition and to develop models of neural representations based on these processing functions. New, flexible stimulus methods will allow the response properties of neurons in SI and SII cortex to be studied systematically. These quantitative studies will be accompanied by theoretical studies aimed at understanding the transformations of spatial information that occur in the somatosensory system at and linking the discharge of cortical neurons to subjects' pattern recognition behavior. In all of the neurophysiological experiments the monkey's attentional state will be controlled and particular attention will be paid to laminar differences in response properties.